Developing renewable sources of feedstocks based on biomass for making distillate products, such as fuels or lubricants, is an area of ongoing interest. Use of biomass as a feedstock source can be attractive from a perspective of avoiding depletion of mineral oil and gas sources. However, a variety of challenges remain in developing technologies for harvesting and processing feeds derived from biomass.
One potential source of biomass-derived feedstocks is algae. Algae is an advantageous form of biomass in part because algae can be grown in artificially constructed ponds. Such algae growth ponds can be placed in desirable locations, such as locations that do not compete with production of food for human consumption. However, algae grown in a pond or other aqueous environment are typically present in a concentration corresponding to a few weight percent of the environment or less. Thus, one of the difficulties with using algae as a biomass source is the need to separate the relatively low concentration of algae from the water which is the majority component of the aqueous environment.
Some previous efforts to separate algae from an aqueous environment have used dissolved air flotation. In a conventional dissolved air flotation method, air is bubbled into an aqueous environment containing algae. The air is bubbled into the aqueous environment with the goal of having the algae attach to or agglomerate on the bubbles. As the bubbles reach the surface of the aqueous environment, algae becomes concentrated at the surface. The surface of the aqueous environment can then be skimmed to capture the algae at the surface. However, the skimming process tends to be inefficient, in part because algae that have traveled to the surface of the aqueous environment can fall back into the bulk portion of the environment. The algae that remain in the aqueous environment pose problems in part due to environmental regulations for the allowable concentration of species in waste water. Additionally, controlling the conditions in the aqueous environment is difficult, as the process is sensitive to small fluctuations within the environment.
Japanese Published Patent Application No. JP 2005261343 appears to describe a variation on dissolved air filtration. Based on the abstract, it appears that water is passed through a horizontal filter in an upward direction. Air bubbles are introduced from the bottom of the aqueous environment. The abstract describes the method as being useful for avoiding clogging of the filter.